Several distinct and high-conserved genes comprise the ras gene family of rodents and humans, i.e., rodent Harvey and Kirsten, and human Harvey, Kirsten and neuroblastoma. Transformation, either by a point-mutation resulting in a change in one amino acid of the 21 kDa ras gene product (p21), or by increased expression of ras p21, has been demonstrated to be mediated by members of this gene family. We have reported the development of direct binding liquid competition radioimmunoassays for the detection and quantitation of the ras oncogene and proto-oncogene products. Using these radioimmunoassays and ras p21 purified from Escherichia coli containing the full-length T24 mutant human Harvey ras gene protein product as a standard, we have defined the actual amount of ras p21 per mu g of total cellular protein, or per cell, in various ras transformed and "normal" mammalian cell lines. Absolute levels of Ha-ras p21 have also been determined in human breast and colon carcinomas, benign lesions, and/or their respective normal tissues using the radioimmunoassays. Enhanced Ha-ras expression was documented in 66% of breast and 100% of colon carcinomas as compared with their normal counterparts, with levels in breast carcinomas ranging from 18.4 to 51.7 pg ras p21 per mu g protein. Some dysplastic lesions of the breast and colon also contained elevated Ha-ras p21. Relative levels of Ha-ras p21 expression, detected by competition RIA, correlated with percent Ha-ras p21 positive cells as determined by immunohistochemical assays. Using liquid competition RIA and immunohistochemical assays, it has been shown that levels of ras p21 expression did not always correlate between primary and metastatic colon lesions of the same patient. The use of the quantitative RIA and semiquantitative immunohistochemical assays, in concert with cDNA probes for identification of specific ras pointmutated oncogenes or protooncogenes, may now provide the means for definitive quantitative analyses of ras p21 in human carcinomas and benign lesions.